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Author Topic: Methods For Tanning Hides  (Read 5446 times)

Offline Askdamice

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Methods For Tanning Hides
« on: January 11, 2008, 07:44:42 AM »
 After accidentally deleating Mistwalker's previous thread (oops) I've started up another one. There was a lot of great info posted in the last one so I hope those folks won't mind retyping their methods.

... And for the new readers.... what we are doing here is sharing techniques used in tanning animal hides. There are many effective ways to do it and there's always something you can learn from someone else's personal experience.


I was taught to use these steps...

1. Fleshing - remove the meat and fat from the hide by scraping.
2. Soaking - soak the hide in either a potash mix or vinegar solution to loosen the hair.
3. Graining - remove the epidermis, hair and fleshside membrane by scraping. Wring out all water, afterwards.
4. Lubricating - rub a lubricant into the hide. (eg. vegetable oil, brains, egg white.)
5. Softening - work the hide by stretching and twisting until it is dry.
6. Smoking - smoke the hide with smoldering plant material to "lock in" the lube, so the hide can be washed while the softnes is still preserved. This step also give the hide that golden tan.

Rick
Rick Marchand
ABS Apprentice Smith
www.wildertools.com
rickmarchand@wildertools.com

Offline mistwalker

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Re: Methods For Tanning Hides
« Reply #1 on: January 12, 2008, 03:07:49 AM »
(eg. vegetable oil, brains, egg white.)
Which one works better?
 
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Offline Askdamice

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Re: Methods For Tanning Hides
« Reply #2 on: January 12, 2008, 07:44:59 AM »
Brains by far... but they are also the hardest to come by if you have the right connections. "If I only had a brain."

The good thing though... is that the hide/brain ratio is perfect if you use the brain from the animal the hide came from.
Rick Marchand
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rickmarchand@wildertools.com

Offline Holly

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Re: Methods For Tanning Hides
« Reply #3 on: January 12, 2008, 08:01:56 AM »
I really liked this article from Wikipedia about the process of tanning.  I'll have to break it down because it's very long, but it tells a history of tanning, why it was done, the processes of tanning, the chemicals used and why those chemicals work.

Tanning is the process of converting putrescible skin into non-putrescible leather, usually with tannin, an acidic chemical compound that prevents decomposition and often imparts color. Tanning leather involves a process which permanently alters the protein structure of skin so that it can not ever return to rawhide. Making rawhide does not require the use of tannin and is made simply by removing the flesh and then the hair by way of soaking in an aqueous solution (often called liming-lime and water or bucking-wood ash and water=lye), then scraping over a beam with a somewhat dull knife, and then leaving to dry, usually stretched on a frame so that it dries flat. The two aforementioned solutions for removing the hair also act to clean the fiber network of the skin and therefore allow penetration and action of the tanning agent.

Ancient Methods of Tanning:

In ancient history, tanning was considered a noxious or "odiferous trade" and relegated to the outskirts of town, amongst the poor. Indeed, tanning by ancient methods is so foul smelling that tanneries are still isolated from those towns today where the old methods are used. The ancients used leather for waterskins, bags, harnesses, boats, armor, quivers, scabbards, boots and sandals. Around 2500 BC, the Sumerians began using leather, affixed by copper studs, on chariot wheels.

Skins typically arrived at the tannery dried stiff and dirty with soil and gore. First, the ancient tanners would soak the skins in water to clean and soften them. Then they would pound and scour the skin to remove any remaining flesh and fat. Next, the tanner needed to remove the hair fibers from the skin. This was done by either soaking the skin in urine, painting it with an alkaline lime mixture, or simply letting the skin putrefy for several months then dipping it in a salt solution. After the hair fibers were loosened, the tanners scraped them off with a knife.

Once the hair was removed, the tanners would bate the material by pounding dung into the skin or soaking the skin in a solution of animal brains. Among the kinds of dung commonly used were that of dogs or pigeons. Sometimes the dung was mixed with water in a large vat, and the prepared skins were kneaded in the dung water until they became supple, but not too soft. The ancient tanner might use his bare feet to knead the skins in the dung water, and the kneading could last two or three hours.

It was this combination of animal feces mixed with decaying flesh that made ancient tanneries so odiferous.

Children employed as dung gatherers were a common sight in ancient cities. Also common were "piss-pots" located on street corners, where human urine could be collected for use in tanneries or by washerwomen. In some variations of the process, cedar oil, alum or tannin were applied to the skin as a tanning agent. As the skin was stretched, it would lose moisture and absorb the agent.

Leftover leather would be turned into glue. Tanners would place scraps of hides in a vat of water and let them deteriorate for months. The mixture would then be placed over a fire to boil off the water to produce hide glue.

Variations of these methods are still used by do-it-yourself outdoorsmen to tan hides. The use of brains and the idea that each animal (except buffalo) has just enough brains for the tanning process have led to the saying "Every animal has just enough brains to preserve its own hide, dead or alive."
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Offline Holly

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Re: Methods For Tanning Hides
« Reply #4 on: January 12, 2008, 08:03:50 AM »

Modern Tanning:

The first stage is the preparation for tanning. The second stage is the actual tanning and other chemical treatment. The third stage applies retanning agents and dyes to the material to provide the physical strength and properties desired depending on the end product.This is known as ( Retanning).The fourth stage is used to apply finishing material to the surface or finish the surface without the application of any chemicals if so desired.This final stage is known as finishing.

Preparing hides begins by curing them with salt.  Curing is employed to check putrifaction of the protein substance (Collagen) because of the chance of bacterial infection due to the the time lag that might occur from procuring it to processing it. It removes the excess water from the hides and skins where water flows from inside because of difference in osmotic pressure. Thus the moisture content of hides and skins get greatly reduced.  In wet-salting, the hides are heavily salted, then pressed into packs for about 30 days. In brine-curing the hides are agitated in a salt water bath for about 16 hours. Generally speaking, methods employed for curing greatly make the chance of bacterial growth unfavorable. Thus curing is also done by preserving the hides and skins at a very low temperature

The hides are then soaked in clean water to remove the salt and mainly to bring back the moisture content to a desirable level so that the hide or skin can be treated with chemicals in an aqueous medium. This process is known as "Soaking" and sometimes a hydrating agent is also employed along with water in a very low percentage for hides and skins which have become very dry.

Liming Process of Hides & Skins

After soaking,the soaked hides and skins are taken for the next operation where these are treated with milk of lime with or without the addition of sharpening agents like sulphide, cyanides, amines etc. The objective of this operation are mainly to

1) Remove the hairs, nails and other keratinous matters
2) Remove some of the interfibrillary soluble proteins like mucins
3) Swell up and split up the fibers to the desired extent
4) Remove the natural grease and fats to some extent
5) Bring the collagen to a proper condition for satisfactory tannage

The weakening of hair is dependent on the break down of the disulphide link of the amino acid called cystine, which is the characteristic of the keratin class of protein like hair and wools. The hydrogen atoms supplied by the sharpening agent reduce the cystine molecule to cystine and the covalent links are ruptured.

The isoelectric point of the collagen is also shifted to around 4.7 due to liming which is more towards an acidic tannage.

Unhairing Agents used during liming are

1) Sodium Sulphide
2)Sodium Hydroxide
3) Sodium Hydrosulphite
4) Arsenic Sulphide
5) Calcium Hydrosulphide
6) Dimethyl Amine
7) Sodium Sulphydrate

The majority of hair is then removed using a machine with remaining hair being removed by hand using a dull knife, a process known as scudding. Depending on the end use of the leather, hides may be treated with enzymes to soften them in a process called "bating". But before bating,the pH of the collagen is brought down to a lower level so that enzymes might act on it. This process is known as "Deliming". Once bating is complete,the hides and skins are treated with a mixture of common salt and Sulphuric acid in case a mineral tanning to be done. This is done to bring down the pH of collagen to a very low level so as to facilitate the penetration of mineral tanning agent into the substance. This process is known as "Pickling". The common salt penetrates the substance twice as fast as the acid and checks the ill effect of sudden drop of pH.

Tanning can be performed with either vegetable or mineral methods. Before tanning, the skins are unhaired, degreased, desalted and soaked in water over a period of 6 hours to 2 days. To prevent damage of the skin by bacterial growth during the soaking period, biocides, such as pentachlorophenol, are used.

Vegetable tanning uses tannin (this is where the name tanning comes from). Tannin occurs naturally in bark. The primary barks used in modern times are chestnut, oak, tanoak, hemlock, quebracho, mangrove, wattle and myrobalan. Hides are stretched on frames and immersed for several weeks in vats of increasing concentrations of tannin. Vegetable tanned hide is flexible and is used for luggage and furniture.

Mineral tanning usually uses chromium in the form of basic chromium sulfate. It is employed after picking. Once the desired level of penetration of chrome into the substance is achieved,the pH of the material is raised again to facilitate the process. This is known as Basification. In the raw state chrome tanned skins are blue and therefore referred to as "wet blue". Chrome tanning is faster than vegetable tanning (less than a day for this part of the process) and produces a stretchable leather which is excellent for use in handbags and garments.

Depending on the finish desired, the hide may be waxed, rolled, lubricated, injected with oil, split, shaved and, of course, dyed. Suedes, nubucks, etc. are finished by raising the nap of the leather by rolling with a rough surface.
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Offline mistwalker

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Re: Methods For Tanning Hides
« Reply #5 on: January 12, 2008, 04:00:24 PM »
Brains by far... but they are also the hardest to come by if you have the right connections. "If I only had a brain."

The good thing though... is that the hide/brain ratio is perfect if you use the brain from the animal the hide came from.
So, can you chill or freeze the brain while you're doing the rest of the process?
 
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Offline mistwalker

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Re: Methods For Tanning Hides
« Reply #6 on: January 12, 2008, 09:13:14 PM »
Also..., exactly what "prep." is involved in getting the brains ready to use?
 
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Offline scafool

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Re: Methods For Tanning Hides
« Reply #7 on: March 01, 2009, 06:52:40 PM »
The Algonquin in Northern Quebec just wash and scrape the moose hide, and they use soap.  They might cook and eat the brains but they don't use them for tanning.
After they have fleshed the hide and took the hair off they they smoke it over a smoldering cedar punk fire so that it will stay soft after it gets wet.
They smoked it by making it into a little wigwam over the smoldering punk that was in a pit. They smoked it until the smoke came all the way through the hide from the inside out. The punk was the kind of rotted cedar wood that breaks into little square cubes.

  After that they work it to break the fiber of the hide.
 Hide breaking is not really about scraping. It is pushing and working the hide as it dries so that the fibers in the hide stay loose. The used blunt tools like paddles instead of sharp tools.
Sometimes they used stone or wooden clubs to beat the hide with glancing blows, just enough to stretch and loosen it.
 As the hide dries the creosote and aldehydes from the smoke combine with the protein of the hide and preserve it. The tars from the smoke water proof the hide so it does not go stiff if it gets wet and dries out again.
 
The major aldehyde in the smoke that tans the leather is formaldehyde (H2CO). It bonds to and makes and cross links with the protein fibers in the hide.
(I am not sure about what other chemicals are in the smoke or just how they work, I assume it is complicated)

Here is a link that tries to describe the natives further north tanning with almost the same method.
( From NWT tourism.)
http://www.nwtarts.com/pdf/tannedhides.pdf

NOTE:
The NWT pamphlet is wrong about the smoking fire.
You don't want hot coals at all.
You want slow smoldering cedar punk only.
It is like cold smoking fish.
If you get heat you will cook the hide instead of curing it.

Not all tribes or families converted everything into buckskins.
In the far north they also tanned with Alder bark.  Hemlock is a very good source of tannic acid too,  maybe even better than Red Oak. 

Another note.
One reason some people used brains, marrow or even the tallow from around the kidneys sometimes, was to get oil into the hide and lubricate it.
 With bark or chemical tanned hides we use either neet's foot oil or sulphated mineral oil. 
Otherwise the leather is like cardboard, hard, brittle and likely to break instead of bend.

Another good tanning chemical is gluteraldehyde. It will tan a hide pure white but it is not natural at all. Leather made with gluteradehyde is so stable that it can be washed in hot water and not cook.